Regen with LiPo Q.

[Geebee]

I just fitted a volt meter to my direct drive brushed motor and discovered it is regenerating on down hills into the LiPo battery pack, will this be a problem if I keep the generated voltage to a max of just under 42 volts into a 36 volt pack?
The ESC does not state that it is meant to regen, but then brushed direct drive with no free wheel isn't that common.

 

[amigafan2003]

Yup - you'll be fine if you're limiting the volts.

 

[wurly]

Sorry to hijack the thread, but seeing as we're talking RC lipo. I've recently added 2 more 5ah packs to my folder (4s2p to make 10ah). I had a problem recently where a cell went bad. After posting on ES about it, it seems i ran the voltage levels too low and only had 5ah. (However i still believe the cell went bad on me).
Endless-sphere.com • View topic - Did i kill my new lipo pack?
So i added 4 new alarms as i could set these alarms at a much higher voltage (3.80V).
I went for a couple short trips t'other day and on the return i could hear one buzzing away. Mmmm low volts already i was thinking!!! after backing off the throttle the volts returned a bit and the alarm stopped. So my questions are, do these packs sag volts enough to give warnings all the time? do i have the alarms set too high? how is it best to monitor these packs?
Baring in mind the controller is a puny 24V ananda limited to 12A, I have a feeling that 10ah isn't going to get me far.

 

[Jeremy]

3.8V is a bit high, as the nominal cell voltage is 3.7V. My experience is that RC cells often sit at around 3.8V per cell, but drop to around 3.7V when fairly well discharged. I tend to work on the basis that 3.6V per cell is a good minimum, but am assured by those who are more adventurous than I that going down to 3V per cell is fine, and some even allow cells to go to 2.8V and get away with it.

If you can set your alarms for 3.6V I think you'll be safe and not get any false alarms.

 

[wurly]

OK thanks Jeremy. Maybe i am a bit fearful of doing permanent damage or causing weakness to the cells i think i'll set them at 3.7V for extra caution. The folder is really used for the convience factor of nipping into town and back rather then longer trips.
I would like to keep the cells at a high(ish) state of charge so the bike can be used at a moments notice, would storage at 4.1 volts be or should that be set lower?

 

[Jeremy]

4.1V is fine for a storage charge. I charge mine to 4.15V and have been running a small 10Ah 10S pack like that for a couple of years now without any problems. I rarely discharge my pack below 3.7V per cell, as I have a little "fuel gauge" that keeps track of the Ah used, and I don't actually bother to measure cell voltage, except as a check before I charge the pack back up again just to make sure all's well.

 

[Geebee]

I have mine set for 3.3v alarm, I don't normally get anywhere near that but it is just a reminder in case I do, or if balance is out by too much.
Make sure you balance the batteries regularly, I find if I fast charge them the balance charger doesn't always get the balance right ( charging faster than it can balance ).
I get around a .1 volt drop per cell drawing 16 amps off a 5 ah, 20c rated pack, as a rough guide.